Automatic optical time-domain reflectometer (otdr)-based testing of device under test

ABSTRACT

In some examples, automatic OTDR-based testing may include determining, based on analysis of a signal that is received from a DUT that is to be monitored, whether the DUT is optically connected. Based on a determination that the DUT is optically connected, a measurement associated with the DUT may be performed.

BACKGROUND

A fiber optic cable may include one or more optical fibers that may beused to transmit light from a source to a destination. The opticalfibers of the fiber optic cable may be referred to as fiber optic links.Fiber optic cables may represent a network element of a fiber opticnetwork. In this regard, other types of network elements may includeoptical connectors, optical splices, optical couplers, and opticalswitches. A fiber optic network may be monitored, for example, by aremote fiber monitoring system that enables oversight of an entire fiberoptic network from a central location. An optical reflectometer such asan Optical Time Domain Reflectometer (OTDR) may be used for testingfiber optic links, and thus a fiber optic cable. The OTDR may operate bysending an optical pulse into the fiber optic link under test, andanalyze the return signal that includes Rayleigh backscatter andreflection signals. The return signal may be analyzed to determineoptical losses along the fiber optic link as well as reflectance fromreflective events. OTDRs may be used, for example, in a stand-alonemode, in a remote controlled mode, or integrated in Telecom or fibermonitoring systems.

BRIEF DESCRIPTION OF DRAWINGS

Features of the present disclosure are illustrated by way of example andnot limited in the following figure(s), in which like numerals indicatelike elements, in which:

FIG. 1 illustrates an architectural layout of an automatic OTDR-basedtesting apparatus in accordance with an example of the presentdisclosure;

FIG. 2A illustrates a case of a correct optical connection, and FIG. 2Billustrates a case of an incorrect optical connection, in accordancewith an example of the present disclosure;

FIG. 3 illustrates an OTDR trace when a device under test is notconnected for the duration of the acquisition, in accordance with anexample of the present disclosure;

FIG. 4 illustrates examples of techniques that can be used to measurethe optical connection quality, in accordance with an example of thepresent disclosure;

FIG. 5 illustrates an example of operation of the automatic OTDR-basedtesting apparatus of FIG. 1, in accordance with an example of thepresent disclosure;

FIGS. 6A and 6B illustrate examples of operation of the automaticOTDR-based testing apparatus of FIG. 1, with respect to detection of anew optical connection and the launch of the OTDR measurement, inaccordance with an example of the present disclosure;

FIG. 7A illustrates a logical flow to illustrate operation of theautomatic OTDR-based testing apparatus of FIG. 1 in case of a singleOTDR connected to a fiber optic link as illustrated in FIG. 5, inaccordance with an example of the present disclosure;

FIG. 7B illustrates a logical flow to illustrate operation of theautomatic OTDR-based testing apparatus of FIG. 1 in case of two OTDRsconnected to opposite ends of a fiber optic link as illustrated in FIG.6B, in accordance with an example of the present disclosure;

FIG. 8 illustrates an example block diagram for automatic OTDR-basedtesting in accordance with an example of the present disclosure;

FIG. 9 illustrates a flowchart of an example method for automaticOTDR-based testing in accordance with an example of the presentdisclosure; and

FIG. 10 illustrates a further example block diagram for automaticOTDR-based testing in accordance with another example of the presentdisclosure.

DETAILED DESCRIPTION

For simplicity and illustrative purposes, the present disclosure isdescribed by referring mainly to examples. In the following description,numerous specific details are set forth in order to provide a thoroughunderstanding of the present disclosure. It will be readily apparenthowever, that the present disclosure may be practiced without limitationto these specific details. In other instances, some methods andstructures have not been described in detail so as not to unnecessarilyobscure the present disclosure.

Throughout the present disclosure, the terms “a” and “an” are intendedto denote at least one of a particular element. As used herein, the term“includes” means includes but not limited to, the term “including” meansincluding but not limited to. The term “based on” means based at leastin part on.

Automatic OTDR-based testing apparatuses, methods for automaticOTDR-based testing, and non-transitory computer readable media forautomatic OTDR-based testing are disclosed herein. The apparatuses,methods, and non-transitory computer readable media disclosed hereinprovide for reduction of the total duration of OTDR measurementsperformed on multiple fiber optic links by reducing, or effectivelyeliminating, the time associated with manual initiation of acquisitions.In this regard, the apparatuses, methods, and non-transitory computerreadable media disclosed herein may utilize permanent (or real-time)OTDR monitoring in order to determine whether a fiber optic link hasjust been physically connected to the OTDR.

With respect to OTDR based monitoring of a fiber optic link, for a fiberoptic cable that includes a plurality of fiber optic links, after eachconnection of the OTDR to a fiber optic link that is to be measured, theOTDR or OTDR based system user may select an option on the OTDR to startthe measurement. This procedure linked to a systematic validation maydepend on the availability and reactivity of the operator, and leads toadditional time that is needed to perform each measurement. The overalltime needed to perform a measurement increases based on an increase in anumber of fiber optic links, and can be substantial for a fiber opticcable that may include tens, hundreds, or thousands of such fiber opticlinks.

A measurement performed by an OTDR may utilize Rayleigh backscatteringand Fresnel reflection signals to monitor events with respect to a fiberoptic network. Due to the relatively low level of the Rayleigh signal,multiple acquisitions may need to be accumulated to obtain a useabletrace to detect or accurately locate and characterize events.

With respect to modern fiber optic cables, an increase in a number offiber optic links per fiber optic cable has direct consequences on thecharacterization time of a fiber optic cable by optical reflectometry.Ribbon fiber optic cables or fiber optic cables with thousands of fiberoptic links may be deployed, and the test time per fiber optic link of afiber optic cable may be specified as a criterion for efficiency.

A certain number of repetitive actions call on the operator of an OTDRfor validation. Thus, after having connected a fiber optic cable (orfiber optic link thereof) to the OTDR, the operator may need to validatethe launch of the OTDR acquisition (e.g., by activating a start key).The operator may effectively verify that the optical connection iseffective by launching a brief acquisition that may be denoted a “realtime acquisition”. This validation operation by the operator can betedious, and time consuming when it needs to be repeated a large numberof times.

The validation operation may need to be performed for stand-alone OTDRs,as well as OTDRs used in a fiber monitoring system. During installationof a fiber monitoring system, a user may need to perform theprovisioning of the fiber monitoring system. The provisioning may beperformed by plugging several optical fiber links to each port of thefiber monitoring system, and manually measuring the optical fiber linksto create reference traces. This process may include connecting severalfiber optic links to each port of the OTDR. For each fiber optic linkconnected to the OTDR, the user may need to manually launch theacquisition of new OTDR traces by pressing a key or equivalent system.It is therefore technically challenging to reduce an overall time neededto perform a measurement associated with the fiber optic link, andparticularly to perform measurements associated with a fiber-optic cablethat may include several fiber optic links.

In order to address the aforementioned technical challenges, theapparatuses, methods, and non-transitory computer readable mediadisclosed herein provide for reduction of the total duration of OTDRmeasurements performed on multiple fiber optic links by reducing thetime associated with manual initiation of acquisitions. In this regard,the apparatuses, methods, and non-transitory computer readable mediadisclosed herein may provide for automatic launching of a referencemeasurement operation, each time a user connects to a fiber optic link.

FIGS. 2A-4 illustrate general principles associated with referencemeasurement of an optical fiber link performed by an OTDR, in accordancewith an example of the present disclosure.

In general, OTDRs perform an optical connection check at the beginningof acquisition to ensure that the connection to a device under test(DUT), such as a fiber optic link, is good. This estimate of theconnection quality can be visualized by a bar graphs of FIGS. 2A and 2B.

Specifically, FIG. 2A illustrates a case of a correct opticalconnection, and FIG. 2B illustrates a case of an incorrect opticalconnection, in accordance with an example of the present disclosure.

Referring to FIG. 2A, a level at an origin 200 of a backscatter trace202 is normal around the reference level usually aligned with the 0 dBgraduation. The bar graph under the trace displays an optical connectionquality qualified as good at 204 (as opposed to bad (or poor) at 206).

The poor connection quality may have different causes such as a dirty,damaged, or an incorrect connection between an OTDR port and a DUT. Forexample, the case of a DUT cut near the OTDR port or the case of anunconnected DUT may result in display of a bad connection on the bargraph. Abnormal insertion loss such as the presence of a curvature or afiber bend on a link fiber between the OTDR and the DUT may also resultin a bad connection.

On the contrary, in the case represented in FIG. 2B, the bar graph belowthe trace displays an optical connection quality qualified as bad at208. The backscatter level at origin 210 has dropped by approximately 8dB degrading the signal to noise ratio on trace 212. A bad connectionmay be signaled by a warning message 214, leaving the user with thechoice to interrupt or not interrupt the current measurement.

FIG. 3 illustrates an OTDR trace when a DUT, such as a fiber optic link,is not connected for the duration of the acquisition, in accordance withan example of the present disclosure.

For example, FIG. 3 shows an example of an OTDR trace 300 when the DUTis not connected for the duration of the acquisition, resulting in a badquality connection as illustrated as 302. In this regard, the signal maydisappear except in the very first few meters 304 due to the response onan open OTDR output connector, or the OTDR connection patchcord to theDUT.

The quality of the connection may be obtained by estimating thebackscatter level at the origin, and comparing the backscatter levelwith predetermined thresholds. These thresholds may vary from product toproduct and from manufacturer to manufacturer.

FIG. 4 illustrates examples of techniques that can be used to measurethe optical connection quality, in accordance with an example of thepresent disclosure.

Referring to FIG. 4, different techniques may be used to measure theoptical connection quality. The level of back-scatter at origin 400,which may be referred to as the injection level, may be estimated byextending up to the horizontal axis a linear regression line 402 appliedto a section of a curve 404 by avoiding the back-reflection at point406. In this regard a reading of the back-scatter level at the start ofcurve 408 may also be used as a reference as it represents thebackscatter level after the first connection between the OTDR and theDUT and therefore may be used as an indicator of the connection qualitybetween the OTDR and the DUT.

Based on the principles disclosed herein with respect to FIGS. 2-4, theapparatuses, methods, and non-transitory computer readable mediadisclosed herein provide for the automatic launch of an OTDR measurementas soon as the optical connection is effective, and without anyintervention by an operator of the OTDR. The apparatuses, methods, andnon-transitory computer readable media disclosed herein may provide fora measuring device, such as an OTDR, to detect connection to a fiberoptic link to be tested, and therefore immediate commencement of ameasurement.

According to examples disclosed herein, the apparatuses, methods, andnon-transitory computer readable media disclosed herein may provide fordetection of the presence of a fiber optic link connected to the OTDR byperforming the analysis of the reflectometric signal, as well asdetection at the optical level of an optical connection. Analysis of thesignal received by the OTDR may be utilized to determine whether the DUT(e.g., fiber optic link) is optically connected.

According to examples disclosed herein, the apparatuses, methods, andnon-transitory computer readable media disclosed herein may provide fordetection of the presence of a fiber optic link connected to the OTDR,without any modification of connection devices (e.g., fiber opticconnectors).

According to examples disclosed herein, the apparatuses, methods, andnon-transitory computer readable media disclosed herein may provide fordetection of the presence of a fiber optic link connected to the OTDR byimplementing an “auto-start” configuration, where the OTDR continuouslyperforms short real-time duration acquisitions and analyzes the signalto detect the presence of a fiber optic link connected to the OTDR. Assoon as the ORDR detects the presence of the optical connection, theOTDR may launch the acquisition (without human intervention) by usingacquisition parameters defined during set-up of the acquisition.

According to examples disclosed herein, the apparatuses, methods, andnon-transitory computer readable media disclosed herein may be utilizedto accelerate the test of multi-fiber fiber optic cables, but also forsequence of measurements on wavelength division multiplexing systems(dense or coarse), as well as bidirectional measurements using twodevices (e.g., two OTDRs) or a single device with a fiber loop at theend. In this regard, a fiber loop may be obtained, for example, by usinga mirror connected to an end of the fiber optic link as the highreflectivity of the mirror will send back the light in the OTDRdirection and enable a bidirectional characterization. Another exampleof a fiber loop may be obtained when the OTDR is connected to adual-fiber optic link, such as where an OTDR is connected with fiberoptic link-1, and an end of fiber optic link-1 is connected to fiberoptic link-2 so that the two fiber optic links connected together loopback to the OTDR location. Performing an OTDR test at each end of thisdual-fiber optic link with such a loop at the end may thus beimplemented by the apparatus 100.

According to examples disclosed herein, the apparatuses, methods, andnon-transitory computer readable media disclosed herein may be appliedwhenever a measurement needs the connection of a fiber optic link beforelaunching the measurement. This connection may be manual, but may alsobe carried out automatically (e.g., without human intervention) via theuse of an optical switch.

With respect to the rapid increase of the number of fibers to bedeployed and tested, according to examples disclosed herein, theapparatuses, methods, and non-transitory computer readable mediadisclosed herein provide for acceleration testing associated with fiberoptic links, and particularly, for a closed project process whereparameters may be set prior to plugging the fiber optic link to betested.

With respect to installation of a monitoring system, a user may need toperform provisioning of a system by plugging the fiber optic links toeach port of the system and manually measuring them to create referencetraces. In this regard, according to examples disclosed herein, theapparatuses, methods, and non-transitory computer readable mediadisclosed herein provide for automation of this operation, where eachtime a user connects a fiber optic link, the reference may be performedwithout further user intervention.

According to examples disclosed herein, with respect to unidirectionaltests, for a single end OTDR that continually performs a real time OTDRacquisition, when a fiber optic link is not connected, the OTDR tracemay be a pulse followed by noise. However, when a fiber optic link isconnected, the OTDR trace may be a pulse followed by the backscatter ofthe fiber optic link (denoted injection level). In this regard, theapparatuses, methods, and non-transitory computer readable mediadisclosed herein provide for detection of injection level for detectionof the fiber optic link presence.

According to examples disclosed herein, with respect to bidirectionaltests, using two instrument, both instruments may send an optical signalin the fiber optic link. If one of the instruments receives a signal ofconnection of the fiber optic link as disclosed herein, this signal maybe utilized by both instruments as a basis to perform testing of thefiber optic link.

According to examples disclosed herein, the apparatuses, methods, andnon-transitory computer readable media disclosed herein may provide forprovisioning and referencing of a monitoring system, without humanintervention.

For the apparatus, methods, and non-transitory computer readable mediadisclosed herein, the elements of the apparatus, methods, andnon-transitory computer readable media disclosed herein may be anycombination of hardware and programming to implement the functionalitiesof the respective elements. In some examples described herein, thecombinations of hardware and programming may be implemented in a numberof different ways. For example, the programming for the elements may beprocessor executable instructions stored on a non-transitorymachine-readable storage medium and the hardware for the elements mayinclude a processing resource to execute those instructions. In theseexamples, a computing device implementing such elements may include themachine-readable storage medium storing the instructions and theprocessing resource to execute the instructions, or the machine-readablestorage medium may be separately stored and accessible by the computingdevice and the processing resource. In some examples, some elements maybe implemented in circuitry.

FIG. 1 illustrates an architectural layout of an automatic OTDR-basedtesting apparatus (hereinafter also referred to as “apparatus 100”) inaccordance with an example of the present disclosure.

Referring to FIG. 1, the apparatus 100 may include a device under test(DUT) connection detector 102 that is executed by at least one hardwareprocessor (e.g., the hardware processor 802 of FIG. 8, and/or thehardware processor 1004 of FIG. 10), to determine, based on analysis ofa signal 104 that is received from a DUT 106 that is to be monitored,whether the DUT 106 is optically connected.

An optical reflectometer controller 108 that is executed by at least onehardware processor (e.g., the hardware processor 802 of FIG. 8, and/orthe hardware processor 1004 of FIG. 10) may perform, based on adetermination that the DUT 106 is optically connected, a measurementassociated with the DUT 106. In this regard, the measurement may beautomatically (e.g., without human intervention) performed upondetection of the optical connection.

According to examples disclosed herein, the DUT 106 may include a fiberoptic link.

According to examples disclosed herein, the DUT connection detector 102may determine, based on analysis of the signal 104 that is received fromthe DUT 106 that is to be monitored, whether the DUT 106 is opticallyconnected by determining, based on analysis of a Rayleigh backscatterpower of the signal 104, whether the DUT 106 is optically connected.With respect to utilization of Rayleigh backscatter power to determinewhether the DUT 106 is optically connected, if the DUT 106 is connected,a part of the power sent by the apparatus 100 will be reflected and, inparticular, the Rayleigh backscattered level will increase because ofthe fiber of DUT 106. This is also illustrated in FIG. 4 where the DUTis connected, compared to FIG. 3 where no DUT is connected.

According to examples disclosed herein, the DUT connection detector 102may determine, based on analysis of the signal 104 that is received fromthe DUT 106 that is to be monitored, whether the DUT 106 is opticallyconnected by determining, based on analysis of a Rayleigh backscatterenergy of the signal 104, whether the DUT 106 is optically connected. Ina similar manner as disclosed herein with respect to the Rayleighbackscatter power, with respect to utilization of Rayleigh backscatterenergy to determine whether the DUT 106 is optically connected, if theDUT 106 is connected, a part of the energy sent by the apparatus 100will be reflected and, in particular, the Rayleigh backscatter energywill increase because of the fiber of DUT 106.

According to examples disclosed herein, the DUT connection detector 102may determine, based on analysis of the signal 104 that is received fromthe DUT 106 that is to be monitored, whether the DUT 106 is opticallyconnected by determining, based on analysis of an Optical Time DomainReflectometer (OTDR) front end backscatter level of the signal 104,whether the DUT 106 is optically connected. With respect to use of theOTDR front end backscatter level of the signal 104 to determine whetherthe DUT 106 is optically connected, if no DUT is connected, there is noRayleigh backscatter level and thus the OTDR front end backscatter levelof the signal 104 is very low. When the DUT 106 is connected, thisconnection results in an increase of the OTDR front end backscatterlevel of the signal 104, and thus a DUT detection may be obtained bycomparing the OTDR front end backscatter level of the signal 104 to athreshold as described below.

According to examples disclosed herein, the DUT connection detector 102may determine, based on analysis of the signal 104 that is received fromthe DUT 106 that is to be monitored, whether the DUT 106 is opticallyconnected by determining, based on comparison of a signal level 110associated with the signal 104 to a reference level threshold 112,whether the DUT 106 is optically connected. For example, referring toFIGS. 2A, 2B, and 3, with respect to the reference level threshold 112,the injection level is approximately 0 dB for a DUT that is properlyconnected as shown in FIG. 2A. The injection level may be a lower valuewhen a DUT is not connected correctly as shown in FIG. 2B, where thelower value is representative of the insertion loss between the OTDR andthe DUT. Further, with respect to FIG. 3, there is no trace and it isnot possible to estimate an injection level when there is no DUTconnected as shown. Thus, the DUT connection detector 102 may generate,based on a determination that the signal level 110 associated with thesignal 104 exceeds the reference level threshold 112, an indication thatthe DUT 106 is optically connected.

According to examples disclosed herein, the optical reflectometercontroller 108 may be executed by the at least one hardware processor toperform, based on a set-up that defines a condition for launch of themeasurement, the measurement associated with the DUT 106. With respectto set-up aspects that define a condition for launch of a measurement,an example may include a user pre-defined threshold for quality of aconnection that will be compared to the signal level 110 in order todetect if the quality of the connection is acceptable or not beforelaunching a measurement.

According to examples disclosed herein, the apparatus 100 (which may bean OTDR), may include a connection port 114. In this regard, the DUTconnection detector 102 may determine, based on analysis of the signal104 that is received from the DUT 106 that is to be monitored, whetherthe DUT 106 is optically connected by determining, based on analysis ofthe signal 104 that is received from the DUT 106 that is to bemonitored, whether the DUT is optically connected to the connection port114.

Operation of the apparatus 100 is described in further detail withreference to FIGS. 5-7B.

FIG. 5 illustrates an example of operation of the apparatus 100, inaccordance with an example of the present disclosure.

Referring to FIG. 5, an OTDR 500 may be used to successively test aplurality (e.g., n) optical fiber links (e.g., fiber optic links 502,504, 506, and 508) via an optical cord 510. Thus, as soon as the OTDR500 is connected to the fiber optic link 502 via optical cord 510, theconnected fiber optic link 502 is detected, and acquisition may beinitiated without human intervention. As soon as the measurement withrespect to the fiber optic link 502 is complete, an operator maydisconnect the fiber optic link 502, and connect the OTDR 500 at point512 to the second fiber optic link 504 to be tested. The presence of anew connection to the fiber optic link 504 may be detected, and lead tothe launch of a new OTDR measurement and so on until all of the fiberoptic links are tested. Thus, the need to launch the acquisition aftereach new connection may be eliminated based on the automated (e.g.,without human intervention) measurement associated with each fiber opticlink.

Compared to the configuration of FIG. 5 which implements unidirectionaltesting associated with a fiber optic link, in bidirectional testing,the fiber optic link characterization technique may utilize thecombination of two instruments (e.g., two OTDRs) connected to both endsof the fiber optic link. In such a configuration, the detection of aconnected fiber optic link may be directly based on the reception of asignal emitted by the second device connected to the remote end. Forexample, the signal emitted by the second device may be similar to thesignal 104 in that the signal emitted by the second device may indicateto the first device that the fiber optic link is also opticallyconnected to the second device.

For example, with respect to bidirectional testing of fiber optic links,FIGS. 6A and 6B illustrate examples of operation of the apparatus 100,with respect to detection of a new optical connection and the launch ofthe OTDR measurement, in accordance with an example of the presentdisclosure. In this regard, the DUT connection detector 102 maydetermine, based on analysis of a further signal that is received fromthe DUT 106 that is to be monitored, whether the DUT 106 is furtheroptically connected an OTDR that is to be optically connected to aremote end of the DUT 106.

Specifically, FIGS. 6A and 6B describe combination of the detection of anew optical connection and the launch of an OTDR measurement. In thecase of FIG. 6A, OTDR 600 is not yet connected to DUT 602 via patch cord604. The OTDR 600 may operate in a monitoring mode for a new opticalconnection, but does not receive any signal emitted by anotherinstrument 606 (e.g., another OTDR or optical source) connected to theremote end of the DUT 602.

Referring to FIG. 6B, when the DUT 602 is connected at 608, the DUTconnection detector 102 may detect that a fiber optic link (e.g., theDUT 602) has just been connected to the OTDR 600 (e.g., by the furthersignal at 610), and may start the acquisition without any humanintervention.

FIG. 7A illustrates a logical flow to illustrate operation of theapparatus 100 in case of a single OTDR connected to a fiber optic linkas illustrated in FIG. 5, in accordance with an example of the presentdisclosure.

Referring to FIG. 7A, at block 700, a measurement set-up of theapparatus 100, which may be an optical reflectometer, such as an OTDR,may be performed. As disclosed in further detail below, if an auto-startmode is enabled for the apparatus 100 and with a measurement set-up thatincludes, for example, a user-predefined threshold, the apparatus 100may compare the backscatter level to this threshold and determine if thequality of the connection is acceptable, and if so, start themeasurement.

At block 702, once the set-up details are entered, OTDR acquisition maybe placed in a start mode to automatically (e.g., without humanintervention) start upon connection of the DUT 106.

Block 704 may represent a high speed connection detection andacquisition launch block. In this regard, at block 706, the DUTconnection detector 102 may perform OTDR trace acquisition with respectto the DUT 106.

At block 708, the DUT connection detector 102 may determine, based onanalysis of a signal 104 that is received from the DUT 106, whether theDUT 106 is optically connected.

At block 710, the DUT connection detector 102 may compare a signal level110 associated with the signal 104 to a reference level threshold 112.

At block 712, the DUT connection detector 102 may determine, based oncomparison (e.g., from block 710) of a signal level 110 associated withthe signal 104 to a reference level threshold 112, whether the DUT 106is optically connected. In this regard, the DUT connection detector 102may generate, based on a determination that the signal level 110associated with the signal 104 exceeds the reference level threshold112, an indication that the DUT 106 is optically connected.

At block 714, if the DUT 106 is optically connected to the apparatus100, the OTDR acquisition may be performed (without any humanintervention). For example, the optical reflectometer controller 108 mayperform, based on a determination that the DUT 106 is opticallyconnected, a measurement associated with the DUT 106. In this regard,the measurement may be automatically (e.g., without human intervention)performed upon detection of the optical connection.

At block 716, the OTDR acquisition may be completed.

Referring again to block 712, if the DUT 106 is not connected,processing may revert to block 706 for continued monitoring of the DUT106 until the DUT 106 is connected. Thus, with respect to blocks706-716, these blocks represent the process for detecting the presenceof a DUT correctly connected to the apparatus 100, and the automaticlaunch of the OTDR acquisition. In this regard, the opticalreflectometer controller 108 may continue to perform OTDR acquisitionsuntil the DUT is disconnected. In order to detect DUT disconnection,blocks 718-724 may provide for detection of DUT disconnection as aprerequisite for a new acquisition.

At block 718, once the OTDR acquisition is completed at block 716, in asimilar manner as block 706, the optical reflectometer controller 108may continue to perform real-time OTDR measurement until the DUT is nolonger connected.

At block 720, in a similar manner as block 708, the DUT connectiondetector 102 may determine, based on analysis of a signal 104 that isreceived from the DUT 106, whether the DUT 106 remains opticallyconnected.

At block 722, in a similar manner as block 710, the DUT connectiondetector 102 may compare a signal level 110 associated with the signal104 to a reference level threshold 112.

At block 724, in a similar manner as block 712, the DUT connectiondetector 102 may determine, based on comparison (e.g., from block 722)of a signal level 110 associated with the signal 104 to a referencelevel threshold 112, whether the DUT 106 remains optically connected. Inthis regard, the DUT connection detector 102 may generate, based on adetermination that the signal level 110 associated with the signal 104exceeds the reference level threshold 112, an indication that the DUT106 remains optically connected, and continue to block 718.Alternatively, if the DUT 106 is no longer optically connected,processing may proceed to block 706 for a new acquisition (e.g., for anew DUT).

With respect to blocks 718 to 724, after performance of the OTDRacquisition at blocks 714 and 716, the optical reflectometer controller108 may perform short real-time measurements at block 718 to detect adisconnection (e.g., at blocks 720 and 722) of the DUT. Thus, when theDUT is disconnected from the apparatus 100 by the user or through anoptical switch, the disconnection may be detected (e.g., at block 724),and the apparatus 100 may be designated as being ready for detection ofa connection of the next DUT (e.g., at blocks 706, 708, etc.).

In order to exit the cycle of successive tests (e.g., several fiberoptic links to be tested successively), such tests may be stopped, forexample, by a user action (e.g., a start/stop key), or after apre-defined number of DUTs being tested (e.g., 12 DUTs for a 12 fiberribbon cable).

FIG. 7B illustrates a logical flow to illustrate operation of theapparatus 100 in case of two OTDRs connected to opposite ends of a fiberoptic link as illustrated in FIG. 6B, in accordance with an example ofthe present disclosure.

Referring to FIG. 7B, at block 726, a measurement set-up of theapparatus 100, which may be an optical reflectometer, such as an OTDR,may be performed. If auto-start mode is enabled, the apparatus 100 maycompare the received signal to a predefined communication sequence. If amatch is obtained between the received signal and the data sequence, theapparatus 100 may automatically detect that another device (e.g.,another OTDR) is connected on the other side of the DUT, and thereforethat the apparatus 100 is itself connected to a DUT so that it may startthe sequence of the measurement.

At block 728, once the set-up details are entered, the apparatus 100 maybe placed in a start mode to automatically (e.g., without humanintervention) start upon connection of the DUT 106.

Block 730 may represent the starting point of a communication sequencewhere the DUT connection detector 102 sends a signal to communicate withthe remote OTDR.

Block 732 may represent a high speed connection detection andacquisition launch block. In this regard, at block 734, the DUTconnection detector 102 may receive a signal (e.g., an emitting signal)from the remote OTDR, and analyze the signal in block 736 in order todetect if the DUT is connected or not connected as disclosed herein withrespect to block 738. With respect to block 738, the signal analysis atblock 738 may include a decoding of the received signal (e.g., aconnection of the remote OTDR may be detected based on detection of apattern associated to communication between two OTDRs or a modulationwhich is characteristic of the communication sequence 730). In such acase, the DUT connection detector 102 may consider that the DUT isconnected as it receives a communication signal. There may be noindicator of the signal quality in such a structure.

At block 738, if the DUT is connected, the DUT connection detector 102may determine, based on signal analysis of the received signal (e.g.,from block 736) of a signal sent by block 734 of the remote OTDR,whether the DUT 106 is optically connected.

At block 740, if the DUT 106 is optically connected to the apparatus100, the communication sequence may be stopped automatically in order tostart the DUT measurement sequence.

At block 742, if the DUT 106 is optically connected to the apparatus100, the OTDR acquisition may be performed (without any humanintervention). For example, the optical reflectometer controller 108 mayperform, based on a determination that the DUT 106 is opticallyconnected, a measurement associated with the DUT 106. In this regard,the measurement may be automatically (e.g., without human intervention)performed upon detection of the optical connection.

At block 744, the OTDR acquisition may be completed.

At block 746, the communication sequence may be resumed between bothdevices (e.g., the apparatus 100 and the remote OTDR). Suchcommunication may be performed to exchange results, or to follow thesequence of measurement depending on the settings defined in measurementsetup at block 726.

At block 748, the apparatus 100 may receive a signal from the remoteOTDR as the communication sequence is resumed with block 746. Forexample, the DUT connection detector 102 may receive a signal from theremote OTDR, and analyze the signal in block 750 in order to detect ifthe DUT is connected or not connected as disclosed herein with respectto block 752.

With respect to block 752, if the DUT is not connected, processing mayproceed to block 732. Alternatively, if the DUT is still connected,processing may revert to block 740.

FIGS. 8-10 respectively illustrate an example block diagram 800, aflowchart of an example method 900, and a further example block diagram1000 for automatic OTDR-based testing, according to examples. The blockdiagram 800, the method 900, and the block diagram 1000 may beimplemented on the apparatus 100 described above with reference to FIG.1 by way of example and not of limitation. The block diagram 800, themethod 900, and the block diagram 1000 may be practiced in otherapparatuses. In addition to showing the block diagram 800, FIG. 8 showshardware of the apparatus 100 that may execute the instructions of theblock diagram 800. The hardware may include a processor 802, and amemory 804 storing machine readable instructions that when executed bythe processor cause the processor to perform the instructions of theblock diagram 800. The memory 804 may represent a non-transitorycomputer readable medium. FIG. 9 may represent an example method forautomatic OTDR-based testing, and the steps of the method. FIG. 10 mayrepresent a non-transitory computer readable medium 1002 having storedthereon machine readable instructions to provide automatic OTDR-basedtesting according to an example. The machine readable instructions, whenexecuted, cause a processor 1004 to perform the instructions of theblock diagram 1000 also shown in FIG. 10.

The processor 802 of FIG. 8 and/or the processor 1004 of FIG. 10 mayinclude a single or multiple processors or other hardware processingcircuit, to execute the methods, functions and other processes describedherein. These methods, functions and other processes may be embodied asmachine readable instructions stored on a computer readable medium,which may be non-transitory (e.g., the non-transitory computer readablemedium 1002 of FIG. 10), such as hardware storage devices (e.g., RAM(random access memory), ROM (read only memory), EPROM (erasable,programmable ROM), EEPROM (electrically erasable, programmable ROM),hard drives, and flash memory). The memory 804 may include a RAM, wherethe machine readable instructions and data for a processor may resideduring runtime.

Referring to FIGS. 1-8, and particularly to the block diagram 800 shownin FIG. 8, the memory 804 may include instructions 806 to determine,based on analysis of a signal 104 that is received from a DUT 106 thatis to be monitored, whether the DUT 106 is optically connected.

The processor 802 may fetch, decode, and execute the instructions 808 toperform, based on a determination that the DUT 106 is opticallyconnected, a measurement associated with the DUT 106.

Referring to FIGS. 1-7B and 9, and particularly FIGS. 7B and 9, for themethod 900, at block 902, the method may include determining, based onanalysis of an emitting signal that is received from an OTDR that isoptically connected to a DUT 106 that is to be monitored, whether afirst end of the DUT 106 is optically connected to a connection port anda second opposite end of the DUT 106 is optically connected to the OTDR.

At block 904, the method may include performing, based on adetermination that the DUT 106 is optically connected to the connectionport and to the OTDR, a measurement associated with the DUT 106.

According to examples disclosed herein, the method may further includereceiving, after completion of the measurement associated with the DUT,a further emitting signal (e.g., see block 748 of FIG. 7B) from the OTDRthat is optically connected to the DUT. Based on analysis of the furtheremitting signal, a determination may be made as to whether the first endof the DUT continues to be optically connected to the connection portand the second opposite end of the DUT continues to be opticallyconnected to the OTDR (e.g., block 752 of FIG. 7B).

According to examples disclosed herein, the method may further includevalidating, based on a determination that the first end of the DUTcontinues to be optically connected to the connection port and thesecond opposite end of the DUT continues to be optically connected tothe OTDR, the measurement associated with the DUT. For example, withreference to FIGS. 7B and 9, once the DUT is determined to be opticallyconnected at block 738, after completion of a measurement at blocks 742and 744, if the DUT is further determined to remain optically connectedto the connection port of the apparatus 100 (e.g., which may be an OTDR)and to the remote OTDR, the determination at block 752 that the DUTcontinues to be optically connected may serve as a validation of themeasurement performed at blocks 742 and 744.

Referring to FIGS. 1-7B and 10, and particularly FIG. 10, for the blockdiagram 1000, the non-transitory computer readable medium 1002 mayinclude instructions 1006 to determine, based on analysis of a signal104 that is received from a DUT 106 that is to be monitored, whether theDUT 106 is optically connected in accordance with a connection qualityspecification.

The processor 1004 may fetch, decode, and execute the instructions 1008to perform, based on a determination that the DUT 106 is opticallyconnected, a measurement associated with the DUT 106.

What has been described and illustrated herein is an example along withsome of its variations. The terms, descriptions and figures used hereinare set forth by way of illustration only and are not meant aslimitations. Many variations are possible within the spirit and scope ofthe subject matter, which is intended to be defined by the followingclaims—and their equivalents—in which all terms are meant in theirbroadest reasonable sense unless otherwise indicated.

1. An apparatus comprising: a device under test (DUT) connectiondetector, executed by at least one hardware processor, to determine,based on analysis of a signal that is received from a DUT that is to bemonitored, whether the DUT is optically connected by determining, basedon comparison of a signal level associated with the signal to areference level threshold, whether the DUT is optically connected; andan optical reflectometer controller, executed by the at least onehardware processor, to perform, based on a determination that the DUT isoptically connected, a measurement associated with the DUT.
 2. Theapparatus according to claim 1, wherein the DUT includes a fiber opticlink.
 3. The apparatus according to claim 1, wherein the DUT connectiondetector is executed by at least one hardware processor to determine,based on analysis of the signal that is received from the DUT that is tobe monitored, whether the DUT is optically connected by: determining,based on analysis of a Rayleigh backscatter power of the signal, whetherthe DUT is optically connected.
 4. The apparatus according to claim 1,wherein the DUT connection detector is executed by at least one hardwareprocessor to determine, based on analysis of the signal that is receivedfrom the DUT that is to be monitored, whether the DUT is opticallyconnected by: determining, based on analysis of a Rayleigh backscatterenergy of the signal, whether the DUT is optically connected.
 5. Theapparatus according to claim 1, wherein the DUT connection detector isexecuted by at least one hardware processor to determine, based onanalysis of the signal that is received from the DUT that is to bemonitored, whether the DUT is optically connected by: determining, basedon analysis of an Optical Time Domain Reflectometer (OTDR) front endbackscatter level of the signal, whether the DUT is optically connected.6. (canceled)
 7. The apparatus according to claim 1, wherein the DUTconnection detector is executed by at least one hardware processor todetermine, based on comparison of the signal level associated with thesignal to the reference level threshold, whether the DUT is opticallyconnected by: generating, based on a determination that the signal levelassociated with the signal exceeds the reference level threshold, anindication that the DUT is optically connected.
 8. The apparatusaccording to claim 1, wherein the optical reflectometer controller isexecuted by the at least one hardware processor to: perform, based on aset-up that defines a condition for launch of the measurement, themeasurement associated with the DUT.
 9. The apparatus according to claim1, further comprising: a connection port, wherein the DUT connectiondetector is executed by at least one hardware processor to determine,based on analysis of the signal that is received from the DUT that is tobe monitored, whether the DUT is optically connected by: determining,based on analysis of the signal that is received from the DUT that is tobe monitored, whether the DUT is optically connected to the connectionport.
 10. A method comprising: determining, based on analysis of anemitting signal that is received from an Optical Time-DomainReflectometer (OTDR) that is optically connected to a device under test(DUT) that is to be monitored, whether a first end of the DUT isoptically connected to a connection port and a second opposite end ofthe DUT is optically connected to the OTDR by determining, based oncomparison of a signal level associated with the emitting signal to areference level threshold, whether the DUT is optically connected to theconnection port and to the OTDR; and performing, based on adetermination that the DUT is optically connected to the connection portand to the OTDR, a measurement associated with the DUT.
 11. The methodaccording to claim 10, wherein the DUT includes a fiber optic link. 12.The method according to claim 10, further comprising: receiving, aftercompletion of the measurement associated with the DUT, a furtheremitting signal from the OTDR that is optically connected to the DUT;and determining, based on analysis of the further emitting signal,whether the first end of the DUT continues to be optically connected tothe connection port and the second opposite end of the DUT continues tobe optically connected to the OTDR.
 13. The method according to claim12, further comprising: validating, based on a determination that thefirst end of the DUT continues to be optically connected to theconnection port and the second opposite end of the DUT continues to beoptically connected to the OTDR, the measurement associated with theDUT.
 14. A non-transitory computer readable medium having stored thereonmachine readable instructions, the machine readable instructions, whenexecuted by at least one hardware processor, cause the at least onehardware processor to: determine, based on analysis of a signal that isreceived from a DUT that is to be monitored, whether the DUT isoptically connected in accordance with a connection qualityspecification by determining, based on comparison of a signal levelassociated with the signal to a reference level threshold, whether theDUT is optically connected; and perform, based on a determination thatthe DUT is optically connected, a measurement associated with the DUT.15. The non-transitory computer readable medium according to claim 14,wherein the DUT includes a fiber optic link.
 16. The non-transitorycomputer readable medium according to claim 14, wherein the machinereadable instructions to determine, based on analysis of the signal thatis received from the DUT that is to be monitored, whether the DUT isoptically connected in accordance with the connection qualityspecification, when executed by the at least one hardware processor,further cause the at least one hardware processor to: determine, basedon analysis of a Rayleigh backscatter power of the signal, a Rayleighbackscatter energy of the signal, or an Optical Time DomainReflectometer (OTDR) front end backscatter level of the signal, whetherthe DUT is optically connected.
 17. (canceled)
 18. The non-transitorycomputer readable medium according to claim 4, wherein the machinereadable instructions to determine, based on comparison of the signallevel associated with the signal to the reference level threshold,whether the DUT is optically connected, when executed by the at leastone hardware processor, further cause the at least one hardwareprocessor to: generate, based on a determination that the signal levelassociated with the signal exceeds the reference level threshold, anindication that the DUT is optically connected.
 19. The non-transitorycomputer readable medium according to claim 14, wherein the machinereadable instructions, when executed by the at least one hardwareprocessor, further cause the at least one hardware processor to:perform, based on a set-up that defines a condition for launch of themeasurement, the measurement associated with the DUT.
 20. Thenon-transitory computer readable medium according to claim 14, whereinthe machine readable instructions to determine, based on analysis of thesignal that is received from the DUT that is to be monitored, whetherthe DUT is optically connected in accordance with the connection qualityspecification, when executed by the at least one hardware processor,further cause the at least one hardware processor to: determine, basedon analysis of the signal that is received from the DUT that is to bemonitored, whether the DUT is optically connected to a connection port.